The log files are collected for a purpose. They are required for troubleshooting a specific issue which may have happened today or even 10 days ago. Generally trace files worth last 10-15 days are sufficient if you are proactive in identifying the issues and opening cases on time. There are a few traces which use up lot of space of they are set to detailed level like the ones below
CUCM---
Cisco Callmanager
Cisco CTIManager
UCCx---
Cisco Unified CCX Engine
The best approach is to set up scheduled trace collection which will transfer the trace files periodically from the cucm or uccx server to an external location thereby freeing up space on your servers on a regular basis. please check below on how to set it up
https://supportforums.cisco.com/document/31766/scheduled-trace-collection-rtmt-cucm-appliance-model
HTH
Manish